Dual bore riser

ABSTRACT

A dual bore riser system is described which includes a conventional monobore riser (12) for production access and an independent coil tubing (14) disposed in parallel with the monobore riser (12) for providing annular access. The monobore riser includes discrete A joints of tubing, casing or drill pipe and the coil tubing riser may be any suitable size but is normally between 23/8&#34; and 27/8&#34; outside diameter. The standard monobore riser (12) and coil tubing riser (14) is fed from a coiled tubing reel (78), which is conventional, via a sheave (80) and straightening rollers into the well with the tubing riser. The coiled tubing is clamped to the tubing riser by clamps (16) at intervals along its length corresponding to a joint every 30 ft. The upper end of the landing spool adaptor (28) receives the tubing (14) and also contains a termination for the coiled tubing which is typically a swage device (32). The 5&#34;×2&#34; landing spool adaptor (28) and landing spool (29) has an 18&#34; outside diameter to fit into the BOP stack (42), and the landing spool (29) has a smooth outside surface for co-operating with the interior of the annular BOP.

The present invention relates to a dual bore riser for use in sub-seaproduction or water or gas injection systems.

Most conventional sub-sea production systems require a dual bore riserto provide access to a larger production bore and an annulus bore whichis smaller. A conventional dual bore riser system consists of a largenumber of parts which require to be assembled during run-in. At thepresent time the cost of a conventional dual bore riser costsapproximately .English Pound.1,000 per foot and requires significantstorage space which is normally limited on off-shore vessels. When sucha conventional riser is run, it requires a considerable amount ofspecialised equipment for handling and make-up such as spiders etc. Thishas an impact in terms of both purchase cost and increased runningtimes.

FIG. 1 shows an exploded view of the principal parts of a conventionaldual parallel bore riser system. It will be seen that approximately tenparts shown, the surface tree, a riser handling spider, a surface treeadaptor joint, a riser tensioning joint, a standard riser joint and ariser handling test tool, a dual parallel bore riser joint adaptor whichis approximately 40 ft. long, an orientation joint, it will be seen fromthis drawing that the entire structure is relatively complex andincludes the assembly of a considerable number of prefabricatedcomponents which, as outlined above, require significant storage spacewhich is normally limited on off-shore vessels.

An object of the present invention is to obviate or mitigate at leastone of the aforementioned disadvantages.

A further object of the present invention is to provide an improved dualbore riser which is relatively less expensive to purchase and to run andwhich requires significantly less storage space than a conventionalriser system.

A further object of the present invention is to obviate the requirementfor specialised handling equipment and make-up of the dual bore riser.

This is achieved by providing a dual bore riser system which comprises aconventional monobore riser for production access and a independent coiltubing disposed in parallel with the monobore riser for providing accessinto the annular space between production coiling and production tubing.The monobore riser comprises discrete joints of tubing, casing or drillpipe and the coil tubing riser which may be any size of coiled tubingbut normally between 23/8" and 27/8" outside diameter.

During deployment of the tubing hanger the standard monobore riser andcoil tubing riser interface with the tubing hanger running tool via alanding spool or adaptor adaptor. The coiled tubing is deployed from astorage reel, via a roller sheave and straightening rollers into thewell with the tubing riser. The coiled tubing is clamped to the tubingriser at intervals along its length corresponding to a joint every 30ft.

The upper end of the landing spool or adaptor receives the tubing andalso contains a termination for the coiled tubing which is typically aswage device. The dual parallel bore landing spool adaptor and landingspool has an outside diameter to fit into the 183/4" BOP stack and thelanding spool has a smooth outside surface for co-operating with theinterior of the annular BOP.

The monobore and coiled tubing risers may be coupled to one of; aconventional stress joint and riser disconnect package to a sub-seaChristmas tree, a dual bore proprietary tubing hanger or a dual boretest tree which fits beneath the blind/shear rams in the BOP stack inthe same manner as disclosed in corresponding International PatentApplication WO93/03255.

According to one aspect of the present invention, there is provided amethod of running intervention equipment into a well during or aftercompletion, said method comprising:

providing well equipment for running into a well, coupling sequentialsections of tubing riser to the well equipment,

providing a coiled tubing riser of smaller diameter than the tubingriser,

coupling the coiled tubing riser to said tool and feeding the coiledtubing riser with the tubing riser to create a structure such that thetubing riser is adjacent and parallel to the coiled tubing,

coupling the coiled tubing riser to the tubing riser at a plurality ofspaced locations along the length of the riser to create a dual boreriser,

and raising or lowering the dual bore riser with the well equipment isrequired for well operations.

Preferably, the method includes restraining the coiled tubing to thetubing riser at each joint along the length of the tubing riser.

Preferably, the dual bore or 5"×2" completion sub-sea tree has a mainbore and a parallel annulus bore, the main bore having at least oneoperable valve and the annulus bore having at least one operable valve.

Conveniently, wireline access is possible using the improved dual boreriser by cutting the coiled tubing at the surface and terminating thecut tubing to a frame and valve assembly which is clamped to aconventional surface tree. The method is such that the frame allows thecoiled tubing to be pretensioned, therefore avoiding the requirement foran accurate termination of the coiled tubing and compensating for anychanges in overall length between the two riser strings. When nowireline operation is required, the coiled tubing may be left on thereel thereby providing annulus communication through the tubing on thereel via a conventional slip ring assembly.

According to another aspect of the present invention there is providedan improved dual bore riser for coupling to intervention well equipmentprior to the installation of a sub-sea production tree, said improveddual bore riser comprising:

a first tubular riser element of a first bore diameter,

a second coiled tubing annulus riser element,

said first and second riser elements being adapted to be connected to awell intervention tool, said first and second riser elements beingcoupled together at a plurality of spaced locations along the length ofthe riser.

Preferably, the second coiled tubing riser is coupled to the firsttubing riser at every riser joint along its length.

Preferably also, the well tool run is a 5"×2" completion sub-sea testtree. Alternatively, the well tool may be any other suitable wellintervention equipment tool.

Conveniently, the coiled tubing is coupled to a landing spool disposedbetween the riser and the completion test tree. The coiled tubing iscoupled to the landing spool via swage and quick connector system andthe tubing riser is coupled to the landing spool via a landing spooladaptor.

A method of forming a dual bore riser for running well interventionequipment, said method comprising the steps of:

providing a plurality of first tubular riser sections of a firstdiameter providing a second coiled tubing annulus riser stored on areel;

coupling said first tubular riser sections together to form a firsttubular riser, unreeling said coil tubing annulus riser from the reel,and

coupling the unreeled tubing riser to the first tubular riser at spacedlocations along the length of the assembled first tubular riser tocreate a dual bore riser.

These and other aspects of the present invention will become apparentfrom the following description when taken in combination with theaccompanying drawings in which:

FIG. 1 is an exploded view of a dual bore riser of a type typicallyfound in prior art systems;

FIG. 2 is a longitudinal assembled view of a tubing landing stringlayout assembled in accordance with a method of the present invention;

FIG. 3a is an enlarged sectional view of top of a landing spool, alanding spool adaptor and depicting how the tubing riser and coiledtubing are coupled to the landing spool adaptor;

FIG. 3b is a cross-section view through the landing spool showing therelative positions of the main production bore and the annulus bore;

FIG. 4 is a longitudinal sectional view through a BOP stack with anintervention tool coupled to an improved dual bore riser in accordancewith an embodiment of the present invention with the riser coupled via a5"×2" sub-sea test tree to a proprietary tubing hanger running tool andtubing hanger;

FIG. 5 is a diagram similar to FIG. 4 but showing 5"×2" completionsub-sea test tree coupled to an Expro test tubing hanger and productioncasing hanger;

FIG. 6 depicts the surface arrangement of the riser and coiled tubingfor permitting wireline access;

FIG. 7 depicts a conventional coiled tubing reel and a sheave withstraightening rolls for receiving coiled tubing from the reel andstraightening the tubing for coupling to the tubing riser shown in FIG.6 and FIG. 3;

FIG. 8 is a schematic representation of an assembled landing stringincluding an improved dual bore riser in accordance with an embodimentof the present invention used in deploying a 5"×2" tubing hanger runningtool;

FIG. 9 is a diagrammatic view of a BOP stack with a tubing hanger runand landed in a wellhead using an improved dual bore riser in accordancewith the present invention, and

FIG. 10 shows an improved dual bore riser in accordance with the presentinvention used in deploying a sub-sea Christmas tree.

Reference is first made to FIG. 2 of the drawings which depicts thelayout of a tubing landing string 10 in accordance with an embodiment ofthe present invention. The string 10 mainly consists of a 51/2" premiumtubing riser 12 and a coiled tubing annulus riser 14 which is coupled tothe tubing riser 12 at various spaced locations along the length of theriser 10 by restraining clamps 16. An umbilical 18 is also coupled tothe riser 10 via the clamps 16. In the layout shown the riser contains alubricator valve 20 at its upper end and retainer valve 22 at anintermediate position and a dual bore sub-sea test tree 24 is located atits lower position. The sub-sea test tree 24 has two ball valves in themain bore and two separate ball valves in the annulus bore. Thecompletion test tree 24 is coupled to dual bore tubing hanger runningtool 44.

The tubing riser 12 and coiled tubing 14 are coupled to the dual borecompletion tree 24 via the landing spool adaptor 28 best shown in FIG. 2and FIG. 3a. The 51/2" tubing riser is received by the landing spooladaptor 28 in a threaded bore 30. The coiled tubing 14 is received in acoil tubing terminator 32 using a conventional coiled tubing swage andconnector system. The landing spool adaptor 28 may receive differentsizes of coil tubing and tubing riser although in the drawings shown thetubing riser is a 51/2 and the coil tubing is 27/8". The landing spooladaptor is coupled to the landing spool 29 via a connector 36 and itwill be seen that the bore 13 of the tubing riser 12 registers with theinternal bore 38 of the landing spool 29. Similarly, the internal bore15 of the coiled tubing registers with the annulus bore 40 of thelanding spool to provide communication in the main bore and in theannulus bores.

Sectional view FIG. 3b taken on the lines X--X of FIG. 3a shows that themain bore 38 offset from the centre of the landing spool, as is annulusbore 40. This arrangement is termed dual bore.

Reference is now made to FIG. 4 of the drawings which is a longitudinalsectional view through a BOP stack 42 which contains a tubing landingstring layout similar to that shown in FIG. 3a disposed in the bore ofthe BOP stack 42. In this case, the riser is coupled to a 5"×2" sub-seatest tree 24 which, in turn, is coupled to a proprietary tubing hangerrunning tool 44 such as Cooper or FMC tool and to a proprietarycompletion tubing hanger 16. It will be seen that the landing stringlayout is spaced out such that the annular BOP 48 can be closed aroundthe exterior of the landing spool 29 to provide an additional annulusbarrier if required. It will be seen that in this case, the space out issuch that the completion tree 24 is disposed beneath the blind/shearrams 50 as disclosed in applicant's copending published PCT applicationWO93/03255.

It will be appreciated that the function of the tubing riser 10 issubstantially identical to that of the 5" section of a standard riser ofthe type shown in FIG. 1 as far as pressure integrity for the well fluidflow and structural capability to run and retrieve the completion teststring is required.

Reference is now made to FIG. 5 of the drawings which is similar to FIG.4 and which shows a dual bore riser coupled via 5"×2" completion sub-seatest tree to an Expro test tubing hanger and a production casing hanger.In this case it will be appreciated that the height of the BOP stackshear rams is not critical but the annular BOP must engage the landingstring 29. It will also be appreciated that like numerals in this figurerefer to the same parts as in FIG. 4.

It will be appreciated that the coil tubing riser is coupled to the51/2" tubing riser approximately every 30 ft. which is the length of atubing riser section. Conveniently, at the same time, the umbilical isalso coupled to the 51/2" tubing riser.

Reference is now made to FIG. 6 of the drawings which depicts thesurface pressure control equipment for a wireline access option into a2" line for tubing hanger plug retrieval. In this case, it will be seenthat the tubing riser 12 is coupled to a 5" surface flow head 60 which,in turn, is coupled to an elevator sub 62 for a lifting frame and to awireline stuffing box 64. The coiled tubing 14 is coupled to a frame 66via a swage connection 68. The function of the frame 66 is to allow thecoil tubing to be pretensioned by exerting a hydraulic force on the dualpistons (65) which is subsequently transferred to the tubing. Thehydraulic pressure is regulated by the use of a gas/liquid accumulatorallowing the pistons to expand and retract and therefore compensate forthe subsequent change in length of the dual risers. The coiled tubingconnection 68 is coupled via a 2" master valve 70 to a T-connection 72which is has an annular inlet 74 on one leg so that annulus fluids canbe pumped through the coiled tubing and the other leg is coupled to ablind cap 76 which can be removed to facilitate wireline entry. It willbe appreciated that if no wireline operations are required, the coiledtubing can be left on the reel, thereby providing annulus communicationsvia a conventional slip ring assembly.

FIG. 7 depicts a conventional coiled tubing reel 78 and tubing 14 istaken from the reel via a curved sheave 80 which includes straighteningrollers (not shown) so that the coiled tubing 14 which leaves the sheathis substantially straight and this, in turn, is coupled to the tubingriser 12 as shown in FIGS. 3 and 6 by clamp 16 at various locationsalong its length after first having been coupled to the landing spooladaptor.

In operation, the riser is run by firstly coupling the desiredarrangement of intervention tools, such as tubing hanger, running tooland completion test tree together. Next the landing spool 29 is coupledto the completion sub-sea test tree 24 and the landing spool adaptor 29is coupled to the landing spool 29. These are held at the surface byconventional tongs and then the first section of the 51/2" tubing riseris coupled to the landing spool via bore 30. Similarly, the leading endof the coiled tubing 14 is coupled to the connector 32 by the swage andquick connector system. Thus, the first part of the riser 10 is formed.The intervention assembly and the riser is then lowered and at the nextsection the coiled tubing is clamped to the tubing riser and also to theumbilical and this is repeated until the riser is of the desired lengthsuch that the correct space out is achieved with the landing spool 29being disposed in the annular BOP 48 and the 5"×2" completion tree 24 isdisposed in the BOP stack 42 such that it is beneath the shear/blindrams 50.

In this position the equipment can be operated as required from surfaceto provide appropriate batch completion and clean ups prior to theinstallation of a sub-sea production tree.

It will be appreciated that a conventional tubing hanger and tubinghanger running tool is only required if the well is suspended with thecompletion in place and the elimination of the items from the system notrequired would provide substantial savings in both operational leadtimeand cost. These items could be replaced by a temporary test hangerassembly which would be run on the lower section valve on the 5"×2"completion test tree and which would allow the tree to lock into thewellhead and obtain an annulus seal via an elastomeric pack off in thecasing hanger or an adaptor bowl within the wellhead.

It will also be appreciated that various modifications may be made tothe method and apparatus hereinbefore described without departing fromthe scope of the invention. For example, it will be appreciated that theimproved dual bore riser may be used to deploy tubing hanger, acompletion, a sub-sea test tree and a sub-sea Christmas tree. Thesealternatives are shown in FIGS. 8, 9 and 10 of the drawings in whichlike numerals refer to like parts.

In FIG. 8 it will be seen that the 5"×2" test tree 24 has an orientationhelical cam profile 82 for mating with a BOP pin for correctly orientingtubing hanger running tool 44. In this case, a completion is run on51/2" tubing using rig-mounted elevators and coiled tubing from thereel.

FIG. 9 shows a tubing hanger run 85 and landed in the sub-sea wellhead84 which is located at the bottom of BOP stack 42 and similarly FIG. 10shows a landing string using 51/2" tubing and coiled tubing coupled to asub-sea conventional Christmas tree 90.

It will be appreciated that the improved dual bore riser in accordancewith the present invention provides significant benefit over theexisting dual bore risers. Firstly it is substantially less expensive,costing between 10%-20% of the existing system, and uses approximatelyonly 15% of the storage space of conventional dual bore risers which isa considerable advantage in off-shore vessels where storage space isusually very limited. The improved dual bore riser does not requirespecialised equipment such as spiders and the like which minimises costand reduces running time because the equipment required for thedeployment of the riser is identical to that used to deploy thecompletion. In addition, the new system offers a considerable reductionin the number of potential leak paths in the annulus system, i.e. fromone every 40" because of previous couplings, to one at each termination.In addition, in conventional risers elastomeric seals are used in themonobore riser and this has been replaced by metal-to-metal connectionsin the 51/2" tubing riser further improving the reliability of thesystem. The use of coiled tubing termination eliminates compressivecoupling normally associated with the proprietary dual bore riser systemand this also minimises the bending imparted to the 5.5" tensilestructural member.

The improved dual bore riser in accordance with the present inventionhas a number of additional advantages. Firstly, it provides additionalisolation barriers by incorporating two valves in the 5"×2" completionsub-sea test tree and the well may be left suspended which provides asubsequent reduction in rig time and formation damage and reduces therole of the BOP to a secondary barrier by avoiding the requirement forthe BOP stack to provide annulus isolation.

We claim:
 1. A method of running intervention equipment into a wellduring or after completion, said method comprising:providing wellequipment for running into a well, coupling sequential sections oftubing riser to the well equipment, providing a coiled tubing riser ofsmaller diameter than the tubing riser, coupling the coiled tubing riserto said well equipment and feeding the coiled tubing riser with thetubing riser into a well such that the tubing riser is adjacent andparallel to the coiled tubing, coupling the coiled tubing riser to thetubing riser at a plurality of spaced locations along the length of theriser to create a dual bore riser, and raising or lowering the dual boreriser with the well equipment as required for well operations.
 2. Amethod as claimed in claim 1 including the further step of restrainingthe coiled tubing to the tubing riser at a joint formed by eachadjoining pair of said sequential sections along the length of thetubing riser.
 3. A method as claimed in claim 1 including the furtherstep of providing the well equipment with a 5"×2" completion sub-seatree which has a mainbore and a parallel annulus bore, the main borehaving at least one operable valve and the annulus bore having at leastone operable valve.
 4. A method as claimed in claim 1 comprising thefurther step of cutting the coiled tubing riser at the surface andcoupling the cut tubing to a frame and valve assembly which is clampedto a conventional surface tree.
 5. A method as claimed in claim 1 toprovide wireline access including the further step of pretensioning thecoiled tubing riser thereby avoiding the requirement for an accuratetermination of the coiled tubing and compensating for any changes inoverall length between the two riser strings.
 6. A method as claimed inclaim 1 including the further step of providing annulus communicationthrough the tubing riser on a reel via a conventional slip ring assemblywhen no wireline operation is required and the coiled tubing riser isleft on the reel.
 7. An improved dual bore riser for coupling tointervention well equipment prior to installation in a sub-seaproduction tree, said improved dual bore riser comprising:a firsttubular riser element of a first bore diameter, a second coiled tubingannulus riser element, said first and second riser elements beingadapted to be connected to a well intervention tool, said first andsecond riser elements being coupled together at a plurality of spacedlocations along the length of the dual bore riser.
 8. A riser as claimedin claim 7 wherein the second coiled tubing riser is coupled to thefirst tubing riser at every riser joint along the length thereof.
 9. Ariser as claimed in claim 7 wherein the well tool run is a 5"×2"completion sub-sea test tree.
 10. A riser as claimed in claim 7 whereinthe coiled tubing is coupled to a landing spool disposed between theriser and the completion test tree.
 11. A riser claimed in claim 7wherein the coiled tubing is coupled to the landing spool via a swageand quick connector system and the tubing riser is coupled to thelanding spool via a landing spool adaptor.
 12. A method of forming adual bore riser for running well intervention equipment, said methodcomprising the steps of:providing a plurality of first tubular risersections of a first diameter; providing a second coiled tubing annulusriser stored on a reel; coupling said first tubular riser sectionstogether to form a first tubular riser; unreeling said coiling tubingannulus riser from the reel; and coupling the unreeled coiled tubingriser to the first tubular riser at spaced locations along the lengththereof to create a dual bore riser.